The present disclosure relates to an image forming apparatus that forms an image on a sheet.
Conventionally, a known image forming apparatus, which forms an image on a sheet, includes a photoconductive drum (an image carrier), a developing device, and a transfer member. An electrostatic latent image formed on the photoconductive drum is developed on a development nip portion by the developing device, and thus a toner image is formed on the photoconductive drum. The transfer member transfers the toner image to a sheet. As the developing device to be applied to such an image forming apparatus, a two-component developing technique using developer including toner and carrier is known.
In the two-component development, the developer is deteriorated due to influences of a number of sheets to be printed, a change in environment, a printing mode (a number of sheets to be sequentially printed per one job), and a page-coverage rate, and thus a toner charging amount changes. Such a phenomenon causes problems such as a decrease in image density, occurrence of tonner fogging, and an increase in toner flying. A conventional technique, which solves such a problem, predicts a change in a charging amount of developer based on a number of sheets to be printed, a change in environment, a printing mode, and a page-coverage rate, and adjusts toner density, a development bias, a surface potential of a photoconductor, a rotational speed of a developing roller, and an output of a suction fan that collects flying toner, thus suppressing a decrease in image density, deterioration of toner fogging, and deterioration of toner flying.
However, such a technique is only a combination of individual predictions under conditions of a number of sheets to be printed, a change in environment, a printing mode, and a page-coverage rate, and thus if a plurality of conditions are changed compositively, it is difficult to sufficiently predict a charging amount of developer.
Therefore, a technique for accurately predicting a charging amount of toner is proposed. In this technique, a surface potential of a photoconductive drum before development and a surface potential of a toner layer on the photoconductive drum after development are individually measured, whereas a toner developing amount is calculated based on an image density measured result on the developed toner layer. The toner charging amount is calculated based on the measured surface potentials and toner developing amount.
In this technique, a value of an electric current flowing into the developing roller that carries developer is measured, and the measured current value is predicted as an amount of toner charges which transfer from the developing roller to the photoconductive drum. A toner developing amount is calculated based on the image density measured result on the developed toner layer. Further, a toner charging amount is calculated based on the amount of toner charges and the toner charging amount.